From the related art, a technology which irradiates a human body surface with an electromagnetic wave by using a Doppler sensor and obtains bio-information included in a reflected wave based on a coordinate plane configured of an I signal and a Q signal of the reflected wave, is known. For example, JP-A-2006-055504 discloses a heart rate measuring apparatus which detects an output signal including an amplitude component and a phase component of a reflected wave from a human body surface by using an electric wave type Doppler sensor, and extracts only a heart rate component by separating the amplitude component generated by body movement of a human body. The heart rate measuring apparatus outputs an amplitude component signal and a phase component signal to a heart rate extractor by performing polar coordinate conversion using an amplitude and phase converter with respect to an output signal (an I signal and a Q signal) including information of the amplitude component and the phase component of the reflected wave output by the electric wave Doppler sensor. The heart rate extractor extracts only accurate heart rate by separating the amplitude component generated by the body movement included in the amplitude component output from the amplitude component signal and the phase component signal by using a method of independent component analysis.
In addition, JP-A-2010-120493 discloses a bio-signal sensing apparatus which prevents deterioration of accuracy of a bio-signal of an occupant. The bio-signal sensing apparatus includes: a sensor unit which senses movement of the occupant by an electric wave type non-modulation Doppler sensor; a bio-signal extract unit which extracts a bio-signal of the occupant based on a phase change of an output of the sensor unit; a distance calculation unit which calculates an estimated distance between the sensor unit and the occupant based on an integrated value of a phase change amount of the output of the sensor unit; and a bio-signal output determination unit which determines reliability of the bio-signal based on the estimated distance and stops the output of the bio-signal in a case where the reliability is low.
The sensor unit includes a local oscillator, a transmission antenna, a receiving antenna, a distributor, or a mixer, and a transmission signal is radiated toward a driver. A local signal T(t) having a frequency fHz expressed by, for example, T(t)=cos(2πft) is emitted from the local oscillator, and a part of the emitted electric wave is reflected and received by the receiving antenna as a receiving signal R(t) approximated by R(t)=cos(2πft−4πd(t)/λ−4πx(t)/λ) (wherein d(x) is a distance displacement between the sensor unit and the driver, x(t) is a fine distance displacement of a body surface including heart rate or respiration of the driver, and λ is a wavelength of the local signal T(t)).
The receiving signal R(t) is distributed into two by the distributor and input into two mixers. In addition, one more local signal T(t) distributed by the distributor is distributed into two in a state where only one phase is shifted by π/4 radian by the distributor, and is input into each of two mixers, and the local signal T(t) and the receiving signal R(t) are mixed with each other. A base band component which is close to a DC region and a modulation component are output by a multiplication operation in the two mixers, but as each of the output signals passes through a low pass filter, a real part Bi(t) and an imaginary part Bq(t) which are expressed as follows in the base band receiving signal including only the base band component, are obtained.Bi(t)=½ cos(4πd(t)/π+4πx(t)/λ)Bq(t)=½ cos(π/4+4πd(t)/λ+4πx(t)/λ)
These parts are converted into a digital signal from an analog signal by an AD converter, and are input to a bio-signal extract unit as a detected signal output by the sensor unit.
In addition, JP-A-2011-015887 discloses a biological state obtaining apparatus or the like which can obtain a bio-signal of a living body in a non-contact manner, and can obtain information related to a biological state without performing complicated processing, such as frequency analysis with respect to a bio-signal. The biological state obtaining apparatus includes: an IQ signal obtaining part which transmits an electromagnetic wave to a body surface of the living body, IQ-wave-detects a reflected wave thereof, and consecutively obtains an I signal and a Q signal which are output from an IQ-wave detector that outputs the I signal and the Q signal in a time series; and a biological state obtaining part which obtains a state of the living body based on a trajectory on an IQ plane of an obtained signal obtained by the IQ signal obtaining part.